Whales and Warming in the Gulf of Maine

As burning fossil fuels pump carbon into the atmosphere and warm Earth’s climate, more than 90 percent of that excess heat is absorbed by the ocean’s surface. Nowhere is this connection clearer than in the Gulf of Maine, where surface waters are warming faster than 99 percent of the global ocean.

New research, however, shows that the Gulf of Maine’s depths are warming even more dramatically — as much as 9 degrees Fahrenheit in parts of the Northeast Channel. This is twice as much as the fastest warming waters at the surface, and it is already reshaping life in the Gulf.

"The magnitude of this warming is extraordinary, and it is clear that there are major processes driving this change," said Barney Balch, a senior research scientist at Bigelow Laboratory for Ocean Sciences. "When you look at the data, you don't have to be a rocket scientist to see this trend in deep water temperatures."

Balch founded the Gulf of Maine North Atlantic Time Series (GNATS), which has systematically sampled the Gulf since 1998. The study uses ships from fishing boats to ferries, and it also includes two autonomous gliders that periodically cross the Gulf while gathering data from the surface to the seafloor, as much as 800 feet down. By sampling the same locations repeatedly, Balch has observed how the Gulf of Maine has warmed and changed over the last two decades.

The dramatic warming that GNATS has captured in the Gulf reflects the interconnectedness of the global ocean. The Northeast Channel funnels water into the Gulf of Maine’s depths from two different sources: the Labrador Current, which bears the cold and fresh signature of melting ice in the Arctic, and the North Atlantic slope, whose water is warm and salty. Climate change has altered circulation patterns in the North Atlantic Ocean, and Balch believes a larger proportion of warm slope water may be entering the Gulf.

"Over the last 20 years, we have detected warm water penetrating increasingly farther west," Balch said. "As this warm water continues to move into the Gulf of Maine, it will directly affect species across the food web and the fisheries that rely on this ecosystem."

Deep warming is already impacting animals in the Gulf, from its smallest to its largest inhabitants. In recent years, North Atlantic right whales have turned up in unexpected places in the Gulf of Maine and beyond, making them more vulnerable to lethal dangers like ship strikes and entanglement in fishing gear.

New research led by Senior Research Scientist Nick Record connects deep water warming trends to a shrinking late-summer supply of right whale's primary prey, the rice-sized copepod Calanus finmarchicus. As the right whales follow this crucial food source, they are foraging well outside of the areas established to protect them. This pattern is especially concerning given that North Atlantic right whales are the second-most endangered marine mammal in the world.

"This deep water warming comes from a different source than the warming taking place at the surface, and these processes will have different — sometimes compounding — consequences," Record said. "Oceanographic models of the year 2100 predict that this warming will continue. What we do between now and then will shape the Gulf of Maine’s future."

PERFECT TIMING

Springtime in the Gulf of Maine brings new life to the base of the food web. Marine algae grow rapidly and a new generation of Calanus finmarchicus copepods hatches and begins to feed on the phytoplankton, sending waves of new energy into the ecosystem.

"Copepods are a critical food source for everything from lobster and fish larvae to right whales in the Gulf of Maine," Senior Research Scientist David Fields said. "They are fatty little snacks that power the entire system and link the surface and deep waters."

After hatching, copepods spend the spring and early summer chowing down on the phytoplankton that live in the upper ocean. By midsummer, their bodies have reached a staggering 70 percent fat — enough to sustain them through a winter without food and produce eggs in the early spring. They migrate more than 500 feet down in the water column to pass the winter hibernating together in dense swarms.

Meanwhile, North Atlantic right whales begin their spring on the move. Traveling back from the calving grounds off the coast of Georgia and Florida, the mothers and new calves reunite with the adult males to feed on copepods in the western Gulf of Maine. In the late summer, the whales move to their feeding grounds at the mouth of the Bay of Fundy, where they feast on the swarms of Calanus hibernating deep in the water column — the perfect high-fat meal before the scarcity of winter.

"The timing of the Calanus finmarchicus life cycle and the way they clump together into groups make them an ideal food source for fish larvae in the spring and whales in the late summer and fall," Fields said. "The Gulf of Maine is beautifully intertwined and synchronous. It is what has made the ecosystem so productive, but also what makes it vulnerable to compounding changes."

In recent years, right whales haven’t found the usual copepod aggregations in their traditional feeding grounds. The deep warming Balch has measured is threatening Calanus’ ability to sustain their dormant phase — the time in their life cycle that is essential for right whales. Warmer waters force the copepods to consume their fat stores faster and wake up earlier, before the bounty of the spring phytoplankton bloom is available to feed the next generation.

"Deep warming is one several problems affecting Calanus and therefore all the animals that rely on them for food," Fields said. "It threatens to uncouple many important relationships in the Gulf of Maine, and we are already seeing changes in the food web."

CHANGE IN THE FORECAST

As right whales fail to find Calanus in their traditional late-summer foraging grounds, they have started searching farther afield, including venturing into unexpected territories around Cape Cod and the Gulf of St. Lawrence. During the summer and fall of 2017, 17 right whales died in these areas — an enormous loss given that the species currently numbers about 400 individuals.

With the species in danger of extinction, people across industries are working together to adapt conservation strategies to protect right whales. In April, representatives from the fishing industry, nonprofit sector, and research community gathered for the semi-annual Atlantic Large Whale Take Reduction Team Meeting, which advises NOAA on actions to minimize right whale mortality. During the meeting, the team was tasked with evaluating strategies to cut the risk of right whale mortalities between 60 and 80 percent. The options for doing so are varied — such as redesigning fishing gear, adjusting the timing of fisheries, and using data to generate new monitoring tools — but each involves trade-offs.

"In some ways, this issue is a microcosm of all the environmental challenges we face, which are often complicated by compelling and competing interests," said Record, who is a member of the Take Reduction Team and participated in the meeting. "The Take Reduction Team sets an example for how groups can work together to tackle these challenges and make effective compromises to reach a common goal."

Much of the April meeting focused on refining a risk assessment model recently designed by NOAA to help inform decisions on the management of fisheries in the Gulf of Maine. As a mathematician and modeler himself, Record believes that models will be an essential part of protecting right whales in the Gulf of Maine — and potentially even helping their population rebound.

The strong connections between deep water warming, Calanus, and right whales offer a promising opportunity to improve conservation. By creating computer models that forecast right whale movement, they could provide a powerful tool for anticipating change and updating management decisions in real-time.

In 2012, Record and collaborators used data about Calanus and oceanographic conditions to develop an algorithm that identified potential right whale habitats. They determined that the region south of Nantucket might be a one such previously unknown area. Recent surveys have revealed the region is indeed a hot spot for the species, and the researchers now hope to develop similar tools to help people predict and prepare for future movement of right whales.

"We're entering a period of uncertainty. The way that right whales are currently moving and exploring new habitats suggests that they are looking for new feeding grounds," Record said. "Forecasting could help us anticipate these movements and respond to environmental changes more proactively."

Good data are critical to accurate predictions, however, and routine measurements to monitor Calanus abundance in the Gulf of Maine have been drastically reduced due to a lack of funding. The research community is working hard to recover this capability, and Record hopes that he may be able to develop models that use alternative data sources to forecast right whale locations, such as monitoring seawater for signs of whale DNA and collecting observations by citizen scientists.

Right whales may keep looking for Calanus in habitats farther and farther afield — but they will soon move into the territory of other copepod species, whose different life cycles make them less appealing prey. The specific life strategies of Calanus finmarchicus and needs of North Atlantic right whales may mean that their fates are intertwined too tightly to separate. Record hopes to partner with Canadian scientists to develop a dynamic conservation strategy — and perhaps one day help the population recover and fill its historical niche in the Gulf of Maine and beyond.

"We will continue to see rapid changes like this among species around the globe," Record said. "We need to study these changes carefully and proactively develop tools that help us protect our environment, and our economy, in a rapidly changing world."

The first image is courtesy of the Anderson Cabot Center for Ocean Life, New England Aquarium. The final image is courtesy of Christin Khan, NOAA, Northeast Fisheries Science Center.